What is happening to A.J. Burnett?

By Bloomberg Sports //

A.J. Burnett’s ERA is higher than it has ever been in his career, and Yankee fans wonder why. At the All-Star break, Burnett holds a 7-7 record with a 4.75 ERA, .85 higher than his career 3.90 mark. And that’s after two straight strong starts to end the first half.

The biggest cause of Burnett’s struggles is a reduction in strikeout rate. From 2008 to 2010, Burnett’s Ks have gone from 9.4/9 IP to 8.5/9 to 6.8/9. Burnett is essentially striking out one-third fewer batters he did in his contract year.

What has led to this trend? One statistic to consider is opponent whiff rate. If batters are swinging and missing less, then it would make sense that Burnett is less capable of striking batters out. During Burnett’s best season in terms of ERA, 2004, his whiff rate was 11.8%. In ’08, his best season in terms of number of wins, his whiff rate was 10.3.% This season: 7.3%.

Besides the decline in whiff rate, there’s also the issue of when those swings and misses transpire. Analyzed by counts, a general trend of lowered whiff rate in each type of count is seen from 2008 through 2010.

However, two numbers seem unusual, and significant, outside of the trend. One, while Burnett’s whiff rate has consistently gone down in a “neutral” count, e.g. 0-0, or 1-1 (from 7.8%, to 7.4%, to 6.4% over the past three seasons) even more drastic is the drop-off in whiff rate with two strikes. In 2008, that number stood at 17.3%; it fell to 14.9% in such situations for 2009, then 12.2% this season. Two, in both 2007 and 2008, Burnett’s whiff rate was higher behind in the count than ahead in the count, though still lower than with two strikes. However, in 2009 and 2010, his whiff rate has been higher ahead in the count than behind in the count, which should actually lead to more strikeouts.

Burnett’s whiff rate should be attributable to a specific part of his game, whether it’s velocity, control, or pitch patterns. While an overall decrease in whiff rate is unlikely to be the result of different pitch patterns, the reduced rate with two strikes, and the reduced percentage behind in the count relative to ahead in the count, may be explained by a difference in pitch trends. One noticeable pitching trend for Burnett is that with two strikes, while even or ahead in the count, he throws consistently more curveballs. However, with the count full, he has gone to his fastball more. Overall, Burnett has become more reliant on his curve with two sstrikes. This decision makes sense for Burnett, considering his curveball is statistically his best pitch in terms of whiff rate percentage this season, at 12.6%. Furthermore, hitters are batting .221 against the curveball, the lowest mark against any of his primary pitches. So, his pitching trends should only help his strikeout numbers improve, not decline.

Is his control impaired then? Actually, his control is the same this season as it has been his entire career. Burnett’s 3.8 BB/9 IP is identical to his career average, and even lower than last year’s “great season” in which he walked 4.2/9 innings. So Burnett’s pitch patterns have shifted, but should have only helped. And yet, he cannot strike people out.

Could the answer then lie in Burnett’s velocity? According to Fangraphs.com, Burnett’s velocity is down this season, averaging 93.2 MPH on his fastball, lower than his career 94.6 average, and way down from the 95.1 average in 2007. Even if Burnett’s velocity has declined, this would only matter if batters swung and missed at the fastball less as a result. However, in the tricky narration that is A.J. Burnett, batters are swinging and missing more often at his slower fastball, and whiffing less often at his curveball compared to years past. This season, batters are swinging and missing 6% of the time against his fastball, compared to 4% in 2009.

On the surface, it’s hard to understand the cause of Burnett’s strikeout struggles. It’s possible Burnett’s reduced fastball velocity is not affecting outcomes on his fastball, but rather on his curve. The velocity differential is reduced between the two pitches, allowing hitters more time to diagnose the curveball and its location. While Fangraphs suggested it’s the location of Burnett’s curveball that’s causing the righty’s problems, we can look at Bloomberg Sports tools to negate this idea.

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We can see from the juxtaposed curveball graphs that generally, Burnett’s curveball has been in the same location, if not slightly lower, which would make sense since he’s throwing more curveballs ahead in the count, a time when he would want to throw that pitch in that location. Thus, it could be that hitters are waiting on the pitch more so than in years past. This becomes evident considering batters are swinging and missing less often against his curveball this year compared to 2009 and 2008.

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